Fundamental Niche Conservatism in the Geographic‐Range‐Expanding Specialist Zodarion rubidum (Zodariidae, Araneae)

ABSTRACT Ecological niche and geographic range concepts are essentially interrelated with the latter being conditioned by species' fundamental ecological tolerances, their intrinsic ability to disperse across landscapes, and the various possible interactions between organisms. Despite local fluctuations in range margin areas, geographic ranges are expected to be relatively stable on a broad scale. Range expansion examples therefore provide good opportunities to understand the importance of dispersal in defining species distributions, and to determine whether fundamental niches are conserved or whether species undergo adaptive evolutionary changes during their expansion. In this study, we investigated the spreading tendencies of the specialist spider, Zodarion rubidum Simon, 1914, comparing different phenotypic traits between three localities from southern, central and northern Europe. We conducted four experiments using field‐collected and laboratory‐reared specimens. We focused on population‐specific locomotory traits, temperature preference and inter‐molt interval at two temperatures, and venom specificity to investigate the species' dispersal abilities and fundamental thermal and dietary niches. We found no indication of spatial sorting, i.e., no highly dispersive phenotypes in the northern population. Moreover, we found no clear indication of changes in the species thermal biology or in venom specificity over space. Specifically, Z. rubidum showed similar temperature preferences between localities, a slower development under warm temperatures in central and northern European populations (possibly reflecting an adaptive shift toward colder temperatures), and a consistent ability to paralyze phylogenetically distant ant species. Overall, we conclude that Z. rubidum spreading might have been human‐mediated and that it does not show major changes in its fundamental niche across space.